Looking down on the canopy, the yellowing appears to make a pattern from the lights.
If that is the case, they may not recover much of the yellowing- but epsom salts (magnesium sulfate) and moving the light away will help.
A dose of nutes containing micro nutrients will address- if it's a secondary deficiency. (zinc, Iron etc.) and in that case the color will return.
I would also, innoculate with a mycorrhiza.
@ 6.5pH is fine for flowering plants, but a flush @6.0pH is a good idea at this point of the grow anyways.